In recent years, electric vehicles such as hybrid electric vehicles that use a combination of an automobile gasoline engine and an electric motor have been progressively developed in order to address environmental problems associated with vehicle emissions.
While in general nickel-hydrogen storage batteries are widely used as the power sources in such electric vehicles, the use of nonaqueous electrolyte secondary batteries is studied to realize power sources having higher capacity and higher output.
In conventional nonaqueous electrolyte secondary batteries, lithium transition metal oxides containing nickel as the main transition metal component are used in positive electrode active materials. However, problems remain in terms of output characteristics and thermal stability.
Patent Literature 1 proposes that a niobium compound is sintered on the surface of a positive electrode active material to enhance output characteristics.
Patent Literature 2 proposes that the surface of a positive electrode active material layer has a nickel oxide containing at least one element selected from the group consisting of aluminum, manganese, magnesium, boron, zirconium, tungsten, niobium, tantalum, indium, molybdenum and tin.